Not applicable.
Not applicable.
1. Field of the Invention
The invention relates generally to the field of connectors for electrical and fiber optic cables. More specifically, the invention relates to connectors used with combined electrical/fiber optic cables such as those used in marine seismic sensor systems, among other applications.
2. Background Art
Fiber optic and combination fiber optic/electrical conductor cables are well known in the art. Such cables include one or more electrical conductors for carrying electrical power and electrical signals, and one or more optical fibers that carry optical signals and/or light from a source such as a laser diode. It is known in the art to use combination fiber optic/electrical cables for marine seismic survey systems. Marine seismic survey systems include a plurality of seismic sensors disposed at spaced apart locations along a cable known as a xe2x80x9cstreamer.xe2x80x9d One or more of such streamers are towed behind a seismic survey vessel in the water. The streamer cable may include one or more optical fibers to carry signals generated by the sensors in response to seismic energy up to recording equipment on the seismic vessel. The streamer may use the one or more electrical conductors to carry electrical power to various signal amplification and processing devices within the streamer. Fiber optic/electrical cables used in marine seismic sensor systems also include some form of xe2x80x9cstrength memberxe2x80x9d, such as a wire rope, steel cable or conventional organic rope to support axial loads as the cable is towed through a body of water. Marine seismic sensor optical/electrical cables also typically include some form of fluid tight sheath or xe2x80x9cjacketxe2x80x9d on the exterior surface to exclude water and other fluids from entering the body of the cable. In some cases, the jacket may be filled with oil of other material that is water resistant and electrically nonconductive.
It is also known in the art to use fiber optic sensors, rather than electrical sensors, for the seismic sensors in a marine seismic streamer. Typically, a number of streamers will be towed in a selected pattern by a seismic vessel and the seismic sensors will be arranged at selected spaced apart positions along each streamer for form a sensor arrangement referred to as an xe2x80x9carray.xe2x80x9d Fiber optic sensor arrays have been disclosed in a number of publications, among them being U.S. Pat. No. 4,648,083 issued to Giallorenzi and entitled, All-Optical Towed and Conformal Arrays, U.S. Pat. No. 4,848,906 issued to Layton entitled, Multiplexed Fiber Optic Sensor and more recently, U.S. Pat. No. 6,084,233 issued to Hodgson et al. entitled, Optical Sensor Array Having Multiple Rungs Between Distribution and Return Buses and Having Amplifiers in the Buses to Equalize Return Signals.
As a practical matter, in order to effectively deploy, transport and store the sensor arrays, it is necessary to be able to easily, reliably and quickly couple and uncouple various components of the array. Thus, it is frequently necessary to couple and uncouple segments of combination fiber optic/electrical cables when such cables are used in the array. Connector assemblies to transmit optical signals from one length of fiber optic cable to another are well known in the art. Additionally, connectors are also known in the art which simultaneously make a number of optical and/or electrical connections via a connector housing containing multiple cavities which locate optical and/or electrical terminals. A system and method for precisely and simultaneously making multiple fiber optic connections for hydrophone arrays is disclosed, for example, in U.S. Pat. No. 5,590,229 issued Goldman et al. entitled, Multichannel Fiber Optic Connector, and in U.S. Pat. No. 6,217,229 issued to Arab-Sageghabadi et al. entitled, Fiber Optic Connector with Dowel Alignment of Mating Members. Numerous United States Military specifications also describe multicavity connectors and fiber optic terminals, including MIL-C-38999, MIL-C-5015 and MIL-T-29504, among others. Telecommunications industry specifications such as GR-326-CORE, Generic Requirements for Single-mode Optical Connectors and Jumper Assemblies, published by Telcordia Technologies, Inc. Piscataway, N.J. 08854, also describe the requirements and features of a series of 1.25 millimeter form factor single and dual terminal optical fiber connectors.
The use of optical fiber in sensor arrays can offer distinct advantages over electrical sensor arrays. In general, optical fiber is able to carry a greater quantity of data over a longer distance than electrical wire. This ability may eliminate or reduce the need for electronics to be located out in the environment away from the seismic vessel or a data receiving station. Additionally, optical fiber is lighter and smaller than the electrical wires necessary to carry an equivalent number of signals. There is also no possibility to develop an electrical short circuit to the seawater environment.
To successfully manage a seismic sensor system it is frequently necessary to divide the array into sections. For example, in a seismic streamer system the system may be divided up into the receiving electronics, shipboard cabling, lead-in or towing cable, and multiple sensor sections. Each of these parts of the system needs to be electrically and/or optically connected to other parts of the system. At each connection between system components, some type of reusable connector is needed to transfer signals and mechanical load across the connection and provide protection of the signal carrying devices from the surrounding environment. The signals may either be electrical or optical, or both. The mechanical loads may be tension, torsion, or bending moment. The environmental protection required may be from fluid pressure, contamination, crush, and shock among others.
As the size and complexity of seismic sensor arrays increases, the number of optical and electrical connections that must be made by the various connectors between system components can increase as well. As the mating connector assemblies are brought together and engaged, the connector simultaneously connects multiple optical terminals. Each optical terminal couples a corresponding end of one optical fiber. Precise alignment of the optical terminals across the connector is necessary for proper optical energy transfer. Proper optical energy transfer is typically defined by the transmitting of optical signals between corresponding optical terminals with a minimum of optical power loss and optical signal back-reflection. Connectors known in the art typically provide optical power loss across the coupling of approximately 0.3 dB maximum and 0.2 dB or less average. Back signal reflection for connectors known in the art typically greater than 40 dB below the transmitted signal.
Precise alignment in connectors known in the art is obtained by allowing the optical terminals to xe2x80x9cfloatxe2x80x9d in a cavity within an insert located in the connector assembly. As the mating terminals as are brought together, they are engaged by an alignment sleeve which, cooperating with the xe2x80x9cfloatxe2x80x9d clearance in the cavity, aligns the terminal axes. To achieve the needed degree of axial alignment of the optical terminals the insert must also be located precisely inside a mechanical housing in both the axial and radial directions. Additionally, a high degree of precision is required to mate the corresponding housings in the axial and radial directions. As a result, very close tolerances are required in the manufacture of components of the typical optical cable connector.
There are further considerations that also affect the cost, complexity and degree of reparability of all optical or electro-optical connector assemblies. One of the considerations is the number of unique parts required to make and assemble the two different genders of the connector assembly. The components of optical cable connectors known in the art are typically completely, or nearly completely, different for male and female parts of the connector. Another consideration is that optical cable connectors known in the art typically do not have a self contained optical service loop. Consequently, when an optical terminal in the connector becomes faulty a total removal and reinstallation of the connector assembly is required, rather than a much simpler and cost effective replacement of the damaged terminal alone. Also, in cases where an electromechanical connector assembly has been converted to either opto-mechanical or electro-opto-mechanical the housing normally provides the backbone for the connector assemblies. This frequently necessitates the near complete disassembly of the connector assembly to access the connector insert. Also, converted connector assemblies do not do a good job of managing optical fiber so as to prevent microbends and kinks.
There is thus a need for a optical cable connector or a combined electrical-optical cable connector that facilitates repairs, reduces the number of gender-specific connector components, and is less expensive to produce and maintain.
One aspect of the invention is a connector for joining two cable ends. The connector includes a load transfer plug adapted to couple to a strength member in the cable. A connector insert assembly is coupled to an inner portion of each load transfer plug. Conductor terminals are disposed in corresponding openings of the connector insert assembly. The terminals protrude from the connector insert assembly. An alignment sleeve holder is coupled to one of the connector insert assemblies. The alignment sleeve holder includes alignment sleeves therein for receiving the protruding terminals. A housing element is coupled to an exterior of each of the load transfer plugs. The housing elements are adapted to coupled to each other and to urge the connector insert assemblies into contact with each other and to transfer axial load between the load transfer plugs coupled to each end of the cable. The housing elements have rotational and axial alignment features on corresponding surfaces thereof. The housing elements are also adapted to be removed from the load transfer plugs without uncoupling the cable from the load transfer plug.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.